Systems With Low-Friction Matte Flexible Printed Circuits

ABSTRACT

An electronic device may include flexible printed circuits. A flexible printed circuit may have metal traces supported by a polymer substrate. The flexible printed circuit may extend between an upper laptop computer housing and a lower laptop computer housing or other structures that move relative to each other in an electronic device. The flexible printed circuit may have a low-friction coating and a matte finish. The flexible printed circuit may have a fluoropolymer coating on the polymer substrate, a fluoropolymer coating on a matte coating on the polymer substrate, a fluoropolymer coating that includes a matting agent on the polymer substrate, a fluoropolymer layer or other polymer layer that is attached to the substrate with a layer of adhesive, a textured surface layer, and/or other structures that help provide the flexible printed circuit with desired physical properties and a desired appearance.

FIELD

This relates generally to electronic devices and, more particularly, toflexible printed circuit structures coupled between components inelectronic devices.

BACKGROUND

Electronic devices often include displays and other components. Thesecomponents may sometimes be mounted in folding lids or other movablehousings structures. A flexible printed circuit cable may be used tocouple components together. For example, a flexible printed circuitcable may be used to couple a display in a laptop computer lid to alogic board in the main housing of the laptop computer.

If care is not taken, flexible printed circuits can be insufficientlyrobust to withstand repeated movement within a housing that has amovable lid or other movable structures, may be unsightly, or may bevulnerable to moisture exposure.

SUMMARY

An electronic device may include flexible printed circuits. A flexibleprinted circuit may have metal traces supported by a polymer substrate.The flexible printed circuit may traverse a gap between an upper laptopcomputer housing and a lower laptop computer housing or other structuresthat move relative to each other or may be used elsewhere in anelectronic device.

The flexible printed circuit may have a low-friction coating that helpsprevent sticking of the flexible printed circuit to structures in anelectronic device such as movable housing structures. The low-frictioncoating may enhance moisture repellency (hydrophobicity). The flexibleprinted circuit may also have a matte finish such as a black mattefinish to enhance the appearance of the flexible printed circuit.

The flexible printed circuit may have a fluoropolymer coating on apolymer substrate, a fluoropolymer coating on a matte coating on apolymer substrate, a polymer substrate with a fluoropolymer coating thatincludes a matting agent, a fluoropolymer layer or other polymer layerthat is attached to a polymer substrate with a layer of adhesive, atextured surface layer, and other structures that help provide theflexible printed circuit with desired physical properties and a desiredappearance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative electronic device suchas a laptop computer in accordance with an embodiment.

FIG. 2 is a cross-sectional side view of an illustrative electronicdevice such as a laptop computer with a flexible printed circuit inaccordance with an embodiment.

FIG. 3 is a cross-sectional side view of an illustrative flexibleprinted circuit in accordance with an embodiment.

FIG. 4 is cross-sectional side view of an illustrative flexible printedcircuit with a coating such as a fluoropolymer coating in accordancewith an embodiment.

FIG. 5 is a cross-sectional side view of an illustrative flexibleprinted circuit with a matte coating layer and a fluoropolymer coatinglayer in accordance with an embodiment.

FIG. 6 is a cross-sectional side view of an illustrative flexibleprinted circuit with a matte fluoropolymer coating in accordance with anembodiment.

FIG. 7 is a cross-sectional side view of an illustrative flexibleprinted circuit to which a tape layer such as a textured blackfluoropolymer tape layer has been attached using adhesive in accordancewith an embodiment.

DETAILED DESCRIPTION

Flexible printed circuits may be used to couple together circuitry inelectronic devices and may be used as substrates to which integratedcircuits and other components may be mounted. An electronic device ofthe type that may include one or more flexible printed circuits is shownin FIG. 1. Device 10 of FIG. 1 may be a handheld electronic device suchas a cellular telephone, media player, gaming device, or other device,may be a laptop computer, tablet computer, or other portable computer,may be a desktop computer, may be a computer display, may be a displaycontaining an embedded computer, may be a television or set top box, ormay be other electronic equipment. Configurations in which device 10 isa device such as a portable computer that has a lid that rotatesrelative to a base may sometimes be described herein as examples. Thisis, however, merely illustrative. Device 10 may be any suitableelectronic equipment.

As shown in the example of FIG. 1, device 10 may have a housing such ashousing 12. Housing 12 may be formed from plastic, metal (e.g.,aluminum), fiber composites such as carbon fiber, glass, ceramic, othermaterials, and combinations of these materials. Housing 12 or parts ofhousing 12 may be formed using a unibody construction in which housingstructures are formed from an integrated piece of material. Multiparthousing constructions may also be used in which housing 12 or parts ofhousing 12 are formed from frame structures, housing walls, and othercomponents that are attached to each other using fasteners, adhesive,and other attachment mechanisms.

As shown in FIG. 1, device 10 may have input-output devices such astrack pad 18 and keyboard 16. Track pad 18 may be formed from a touchsensor that gathers touch input from a user's fingers. Keyboard 16 mayhave an array of keys 16K that protrude through openings in the upperwall of housing 12B. Device 10 may also have components such as acamera, microphones, speakers, buttons, status indicator lights,sensors, and other input-output devices. These devices may be used togather input for device 10 and may be used to supply a user of device 10with output. Ports in device 10 may receive mating connectors (e.g., anaudio plug, a connector associated with a data cable such as a UniversalSerial Bus cable, a data cable that handles video and audio data such asa cable that connects device 10 to a computer display, television, orother monitor, etc.).

Device 10 may include a display such a display 14. Display 14 may be aliquid crystal display (LCD), a plasma display, an organiclight-emitting diode (OLED) display, an electrophoretic display, or adisplay implemented using other display technologies. A touch sensor maybe incorporated into display 14 (i.e., display 14 may be a touch screendisplay) or display 14 may be insensitive to touch. Touch sensors fordisplay 14 may be resistive touch sensors, capacitive touch sensors,acoustic touch sensors, light-based touch sensors, force sensors, ortouch sensors implemented using other touch technologies.

Device 10 may have a one-piece housing or a multi-piece housing. Asshown in FIG. 1, for example, electronic device 10 may be a device suchas a portable computer or other device that has a two-part housingformed from an upper housing portion such as upper housing 12A and lowerhousing portion such as lower housing 12B. Upper housing 12A may includedisplay 14 and may sometimes be referred to as a display housing or lid.Lower housing 12B may sometimes be referred to as a base housing or mainhousing.

Housings 12A and 12B may be connected to each other using hingestructures located in region 20 along the upper edge of lower housing12B and the lower edge of upper housing 12A. For example, housings 12Aand 12B may be coupled using hinges 26. Hinges 26 may be located atopposing left and right edges of housing 12 along hinge axis 22. Aslot-shaped opening such as opening (slot) 30 may be formed betweenupper housing 12A and lower housing 12B and may be bordered on eitherend by hinges 26. Hinges 26 may allow upper housing 12A to rotate aboutaxis 22 in directions 24 relative to lower housing 12B. The plane of lid(upper housing) 12A and the plane of lower housing 12B may be separatedby an angle that varies between 0° when the lid is closed to 90°, 140°,or more when the lid is fully opened.

Devices such as device 10 of FIG. 1 may include printed circuits. Theprinted circuits may contain signal paths formed from metal traces(e.g., traces of copper, gold, other metals, etc.) and insulatingsubstrate layers. The printed circuits may include rigid printed circuitboards (e.g., printed circuits formed from fiberglass-filled epoxy orother rigid printed circuit board substrate material) and flexibleprinted circuits (e.g., printed circuits formed from flexible sheets ofpolymer such as layers of polyimide or other flexible polymer substratematerial). Integrated circuits, connectors, discrete components (e.g.,inductors, capacitors, and resistors), and other electrical componentsmay be coupled to printed circuits such as flexible printed circuits(e.g., using conductive connections formed from solder, conductiveadhesive, or other conductive material). Flexible printed circuits mayalso be used as signal paths for routing signals between differentlocations in an electronic device. For example, a flexible printedcircuit such as flexible printed circuit 32 of FIG. 1 may be used toroute signals between display 14 and circuitry 34 across gap 30.Circuitry 34 may include integrated circuits and/or other circuitcomponents mounted to a logic board to which printed circuit 32 iscoupled or integrated circuits and/or other circuit components mountedon an end portion of printed circuit 32 (e.g., circuitry 34 may includestorage and processing circuitry such as a microprocessor, a graphicsprocessing unit, and/or other circuitry for supporting the operation ofdevice 10). Flexible printed circuit cables may be used to couple logicboards and other circuits to components such as touch sensors, may beused in interconnecting logic boards, may be used in routing signalsbetween a logic board and a camera module or other components in device10, and/or may be used to convey signals between other circuitry indevice 10.

In some arrangements, printed circuits may be visible to a user of anelectronic device and/or may experience repeated bending and unbendingstress. Consider, as an example, the arrangement of FIG. 1 in whichflexible printed circuit 32 extends between upper housing 12A and lowerhousing 12B. A cross-sectional side view of a portion of device 10 ofFIG. 1 taken along line 40 and viewed in direction 42 is shown in FIG.2. As shown in the illustrative cross-sectional side view of device 10of FIG. 2, a viewer such as user 44 may view portion 32P of flexibleprinted circuit 32 through housing openings such as gap 48 in direction46 when upper housing 12A is in an open position relative to lowerhousing 12B (as an example). During use of device 10, a user may openand close device 10 repeatedly. As upper housing 12A is opened andclosed (e.g., by rotating housing 12A relative to housing 12B indirections 24 relative to axis 22), flexible printed circuit 32 may berepeatedly bent back and forth. In an open configuration such as theillustrative configuration of FIG. 2, the surface of flexible printedcircuit 32 that faces curved surface 12AC of housing 12A may bestretched against curved surface 12AC. As a result, there is a risk thatflexible printed circuit 32 will stick to surface 12AC.

As a result of these concerns, it may be desirable to provide flexibleprinted circuit 32 with a number of enhanced visual and mechanicalattributes. For example, it may be desirable to provide flexible printedcircuit 32 with a matte appearance (e.g., a dark low gloss appearance)so that portion 32P of flexible printed circuit is visually attractive(e.g., not too bright and shiny). To sustain repeated bending as housing12 is opened and closed, it may be desirable to form flexible printedcircuit 32 from structures that are sufficiently robust to withstandrepeated flexing and possible punctures from external objects thatprotruded through openings such as opening 48. To ensure that flexibleprinted circuit 32 does not stick to a surface such as surface 12AC, itmay be desirable to provide flexible printed circuit 32 with alow-friction surface that exhibits low adhesion to surface 12AC. Asurface such as a low-adhesion surface may be moisture repellant (e.g.,flexible printed circuit 32 may be hydrophobic) and may thereforesometimes be referred to as a nonstick or hydrophobic surface.

A cross-sectional side view of an illustrative printed circuit of thetype that may be provided with attributes such as these is shown in FIG.3. A printed circuit for device 10 such as printed circuit 32 of FIG. 3may be a rigid printed circuit board, may be a rigid flex circuit thatcontains both rigid printed circuit board portions and flexible printedcircuit portions, or may be a flexible printed circuit that does notinclude any rigid printed circuit board portions. Illustrativeconfigurations in which printed circuit 32 is a flexible printed circuitwithout rigid portions may sometimes be described herein as an example.

As shown in FIG. 3, flexible printed circuit 32 may have a substratesuch as substrate 50. Substrate 50 may include one or more layers ofpolyimide or other flexible sheets of polymer material. These sheets ofmaterial may be laminated together using interposed layers of adhesive(as an example). Patterned metal traces 52 (e.g., lines, vias, andcontact pads formed from copper and/or other metals) may be used tocarry signals in flexible printed circuit 32. For example, flexibleprinted circuit 32 may include metal traces such as solder pads 52P towhich connectors, integrated circuits, and other components 54 may besoldered (e.g., using mating solder pads 54P on components 54 and solder56). Conductive connections to traces 52 in flexible printed circuit 32may also be made using conductive adhesive and/or other electricalcoupling mechanisms.

There may be any suitable number of components 54 coupled to flexibleprinted circuit 32. For example, flexible printed circuit 32 may be usedsolely as a signal bus cable and may have connectors mounted at each endand no intervening circuit components soldered to traces 52 along thelength of flexible printed circuit 32. As another example, flexibleprinted circuit 32 may be populated with 2-10, more than 3, fewer than20 or other suitable number of electrical components (connectors,integrated circuits, discrete components, etc.). In some configurations,flexible printed circuit 32 may serve both as a component mountingsubstrate for integrated circuits (e.g., display driver circuitry, etc.)and as a cable (e.g., a cable that extends across an housing openingsuch as gap 30 of FIG. 1).

Components 54 may, if desired, be mounted to both sides of flexibleprinted circuit 32 (e.g., both upper and lower surfaces of flexibleprinted circuit 32). Flexible printed circuit 32 may have an elongatedoutline (e.g., flexible printed circuit 32 may form an elongated strip)and/or may have a more compact (e.g., square) layout. Configurations inwhich flexible printed circuit 32 has a non-elongated portion and anelongated tail or tails extending outwardly from the non-elongatedportion may also be used.

The upper and/or lower surfaces of flexible printed circuit 32 may beprovided with coatings to enhance the performance of flexible printedcircuit 32. These coatings may, for example, improve the appearance offlexible printed circuit 32 by reducing the shininess (gloss) offlexible printed circuit 32 and/or may improve the mechanical propertiesof flexible printed circuit 32 (e.g., by reducing friction and thereforestickiness while increasing hydrophobicity, enhancing durability, etc.).As shown in the illustrative configuration of FIG. 4, flexible printedcircuit 32 may have coatings such as layers 58 on substrate 50. Ingeneral, coatings may be formed on one or both sides of flexible printedcircuit 32. In the example of FIG. 4, coating 58 has been formed on boththe upper and lower surfaces of substrate 50. In other examples (see,e.g., FIGS. 5, 6, and 7) layers have been formed on one side ofsubstrate 50.

Coating 58 of FIG. 4 may be a low-friction coating (e.g., a coating thatreduces the friction and adhesion properties of flexible printed circuit32 relative to that of substrate 50). Low friction may generally becorrelated with low stickiness (low adhesion) and hydrophobicity.Accordingly, it may be desirable for coating 58 to exhibit enhancedhydrophobicity. The amount of hydrophobicity of flexible printed circuit32 may be quantified in terms of water contact angle. As an example,substrate 50 may be characterized by a water contact angle of 81° to 95°without any coatings (i.e., substrate 50 may not be hydrophobic whenuncoated). To ensure that flexible printed circuit 32 is hydrophobic(e.g., to raise the water contact angle of flexible printed circuit 32above 100°), coating 58 may be formed on substrate 50. Coating 58 maybe, for example, a fluoropolymer coating. An example of a fluoropolymercoating is perfluoropolyether. Other fluoropolymers that enhance thehydrophobicity of printed circuit 32 may be used, if desired. Theresulting water contact angle of flexible printed circuit 32 of FIG. 4when coating 58 is formed on substrate 50 may be at least 100°, at least105°, at least 110°, or other elevated value. In general, low-frictionhydrophobic coatings for printed circuit 32 such as coating 58 may beformed from oil, dry lubricants, silicone spray coatings, or any othernon-stick materials.

The surface of substrate 50 may have an associated gloss value. Forexample, a non-matte polyimide substrate 50 may have a gloss value of 25gloss units at 60° and a gloss value of 43 gloss units at 85° (and awater contact angle of 81°) when substrate 50 is uncoated or may have agloss value of 10 gloss units at 60° and a gloss value of 27 units at85° when substrate 50 is uncoated and a matte uncoated polymer substrate50 may have a gloss value of 3 gloss units at 60° and 28 gloss units at85° (and a water contact angle of 95°) when uncoated.

The appearance of flexible printed circuit 32 may be enhanced byreducing the shininess and brightness of flexible printed circuit 32(e.g., by lowering the gloss value of printed circuit 32 and/or byforming a dark surface for printed circuit 32). With one illustrativeconfiguration, a matte coating (e.g., a black matte coating) may beincorporated into flexible printed circuit 32. As shown in FIG. 5, forexample, matte coating layer 60 may be formed on the surface ofsubstrate 50 (e.g., a polyimide layer). Matte coating layer 60 may beuncovered by additional coating layers or may, as shown in FIG. 5, becoated with a low-friction coating such as fluoropolymer layer 58 toenhance hydrophobicity. Matte coating layer 60 may be formed from apolymer (e.g., epoxy, etc.) that includes light-absorbing pigment forreducing the brightness of layer 60 and that includes matting agentssuch as light-scattering particles that enhance the surface roughness oflayer 60 and/or otherwise reducing the gloss value of flexible printedcircuit 32. For example, flexible printed circuit 32 of FIG. 5 may becharacterized by a gloss value of less than 18 gloss units (or less than25 GU, less than 20 GU, or other suitable value) at 60° and may becharacterized by a gloss value of less than 32 gloss units (or less than43 GU, less than 40 GU, less than 35 GU, or other suitable value) at85°. The color of layer 60 may be adjusted by incorporating blackpigment or other colorant into layer 60 (e.g., so that layer 60 is matteblack, etc.). The presence of layer 58 may help ensure that the watercontact angle of flexible printed circuit 32 of FIG. 5 is at least 105°or at least 100° (as examples). The presence of matte coating layer 60may help ensure that the appearance of flexible printed circuit 32 isnot too shiny.

Matte coating materials and fluoropolymer materials may be combined in asingle coating layer (or multiple coatings) as shown by mattefluoropolymer coating layer 62 on substrate 50 in illustrative flexibleprinted circuit 32 of FIG. 6. With this type of arrangement, darkpigment, matting agents, light scattering particles, and/or othermaterials for reducing the gloss of flexible printed circuit 32 may becombined and used in forming a fluoropolymer layer such as layer 62 onsubstrate 50. This may provide flexible printed circuit 32 with a glossof 1 gloss unit (or less than 25 GU, less than 20 GU, less than 10 GU,less than 5 GU, or other suitable value) at 60° and a gloss value of 3-6gloss units (or less than 43 GU, less than 25 GU, less than 20 GU, lessthan 10 GU, less than 5 GU, or other suitable value) at 85° (as anexample). If desired, flexible printed circuit 32 of FIG. 6 may betextured (e.g., using the matting agents in layer 62 and/or by using atexturing drum or other equipment to impart a texture to the surface oflayer 62). The texturing of layer 62 and/or the inclusion of mattingagents into layer 62 may enhance hydrophobicity for flexible printedcircuit 32 of FIG. 6. For example, the water contact angle of flexibleprinted circuit 32 of FIG. 6 may be enhanced to a value of at least100°, at least 110°, at least 120°, at least 130°, at least 140°, or atleast 150°. For at least some of these values (e.g., 150°), flexibleprinted circuit 32 will exhibit extreme hydrophobicity, low friction,and lack of stickiness that help prevent flexible printed circuit 32from adhering to housing structures in device 10, etc. The ability torepel moisture from flexible printed circuit 32 may also help preventmoisture damage in device 10.

If desired, a layer of polymer may be attached to substrate 50 usingadhesive. The added layer may provide enhanced robustness,hydrophobicity, opacity, low gloss, and/or other desired attributes. Inthe illustrative configuration of FIG. 7, a textured hydrophobic sheet(layer 64) has been attached to substrate 50 by an interposed layer ofadhesive 66 (e.g., a layer of pressure sensitive adhesive or otheradhesive). Layer 64 may be textured by processing the surface of layer64 with a textured drum or using other layer texturing techniques tohelp enhance hydrophobicity and/or reduce gloss or, if desired, layer 64may have an untextured surface. Layer 64 may be formed from afluoropolymer such as polytetrafluoroethylene (as an example) to enhancehydrophobicity. Pigment may, if desired, be incorporated into layer 64and/or matting agent may be incorporated into layer 64 to adjust theappearance of layer 64 (e.g., black pigment, matting agent to reduce theglass of layer 64, etc.). With one illustrative configuration, layer 64and layer 66 form a tape layer (e.g., a black polytetrafluoroethylenetape layer with or without texture) and may be attached to layer 50 bylamination. The thickness of this tape layer may be 10-150 microns, morethan 5 microns, less than 100 microns, or other suitable thickness. Thetape layer attached to layer 50 may be formed along only part of thelength of flexible printed circuit 32 (e.g., visible portions, portionsthat bend and/or that are visible to a user such as portion 32P of FIG.2) and/or the tape layer may be formed over the entire surface offlexible printed circuit 32. If desired, the tape layer may be formedfrom a length of flexible printed circuit 32 (e.g., a printed circuitwith metal traces, hydrophobic surfaces, matte surfaces, etc.).

The coating arrangements of FIGS. 4, 5, 6, 7 may be used to cover onesurface or both upper and lower surfaces of flexible printed circuit 32.Moreover, polymer tape layers such as layer 64 of FIG. 7 may be formedusing a single layer of a fluoropolymer (e.g., layer 58 of FIG. 4),using a matte coating such as coating 60 of FIG. 5 that is optionallycoated with layer 58, using a matte fluoropolymer layer such as layer 62of FIG. 6, using a drum-textured or other textured polymer layer (e.g.,a black fluoropolymer layer such as a polytetrafluoroethylene layer orother layer that contains optional matting agent and that is optionallyattached to substrate 50 with a layer of pressure sensitive adhesive orother adhesive), and/or using other suitable structures for reducinggloss, enhancing opacity (enhancing blackness and thereby reducingvisibility), enhancing hydrophobicity (lowering adhesion and friction),and/or enhancing strength (robustness during bending, resistance topunctures, etc.). The configurations of FIGS. 4, 5, 6, and 7 are merelyillustrative. The surfaces of flexible printed circuit 32 may behydrophobic (e.g., the water contact angle of printed circuit 32 may beat least 100°, at least 110°, at least 130°, at least 150°, or othersuitable value) and/or may exhibit low gloss (e.g., a gloss at 60°and/or 85° of less than 10 gloss units, less than 5 gloss units, lessthan 3 gloss units, less than 2 gloss units, less than 1 gloss unit,etc.).

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

1. A flexible printed circuit, comprising: a polymer substrate; metaltraces in the polymer substrate; and a hydrophobic layer on the polymersubstrate.
 2. The flexible printed circuit defined in claim 1 whereinthe hydrophobic layer comprises a layer of hydrophobic polymer attachedto the polymer substrate with a layer of adhesive.
 3. The flexibleprinted circuit defined in claim 2 wherein: the polymer substratecomprises polyimide; and the hydrophobic polymer comprisespolytetrafluoroethylene.
 4. The flexible printed circuit defined inclaim 2 wherein the layer of hydrophobic polymer comprises a blacktextured polytetrafluoroethylene layer.
 5. The flexible printed circuitdefined in claim 1 wherein the hydrophobic layer comprises afluoropolymer layer having a water contact angle of at least 105°. 6.The flexible printed circuit defined in claim 5 further comprising amatte polymer layer interposed between the polymer substrate and thefluoropolymer layer, wherein the fluoropolymer layer on the polymersubstrate with the matte polymer layer interposed between the polymersubstrate and the fluoropolymer layer has a gloss value of less than 20gloss units at 60°.
 7. The flexible printed circuit defined in 5 whereinthe fluoropolymer layer includes matting agent and exhibits a glossvalue of less than 2 gloss units at 60°.
 8. The flexible printed circuitdefined in claim 1 wherein the hydrophobic layer comprises a blackfluoropolymer layer having a water contact angle of at least 110°. 9.The flexible printed circuit defined in claim 8 wherein the blackfluoropolymer layer includes a matting agent, wherein the blackfluoropolymer layer has a gloss value of less than 2 gloss units at 60°,and wherein the black fluoropolymer layer has a water contact angle ofat least 150°.
 10. A portable computer, comprising: a metal housinghaving an upper housing portion that contains a display and having alower housing portion; first and second hinges that connect the upperhousing portion to the lower housing portion, wherein the upper andlower housing portions are rotatable with respect to each other;circuitry in the lower housing portion; and a hydrophobic flexibleprinted circuit that is coupled between the circuitry in the lowerhousing portion and the display in the upper housing portion.
 11. Theportable computer defined in claim 10 wherein the hydrophobic flexibleprinted circuit includes a polymer substrate and a hydrophobic layer onthe polymer substrate.
 12. The portable computer defined in claim 11wherein the hydrophobic layer comprises a fluoropolymer coating on thepolymer substrate.
 13. The portable computer defined in claim 12 whereinthe hydrophobic layer is characterized by a water contact angle of atleast 130°.
 14. The portable computer defined in claim 11 wherein thehydrophobic layer comprises a fluoropolymer layer attached to thepolymer substrate by a layer of adhesive.
 15. The portable computerdefined in claim 14 wherein the fluoropolymer layer comprises a layer oftextured black polytetrafluoroethylene.
 16. The portable computerdefined in claim 11 wherein the hydrophobic layer comprises afluoropolymer layer and wherein the flexible printed circuit furthercomprises a matte coating layer between the polymer substrate and thefluoropolymer layer.
 17. The portable computer defined in claim 11wherein the hydrophobic layer comprises a fluoropolymer coating with amatting agent and wherein the fluoropolymer coating with the mattingagent has a gloss value of less than 10 gloss units at 85°.
 18. Aflexible printed circuit, comprising: a polymer substrate containingmetal traces; and a fluoropolymer coating on the polymer substrate,wherein the fluoropolymer coating has a water contact angle of at least130°.
 19. The flexible printed circuit defined in claim 18 wherein thefluoropolymer coating comprises a matting agent and wherein thefluoropolymer coating exhibits a gloss at 60° of less than 2 glossunits.
 20. The flexible printed circuit defined in claim 18 wherein thefluoropolymer coating comprises a black fluoropolymer coating.